This invention relates to retractable trailer hitches for railroad cars used to transport over-the-road trailers, and, more particularly, to a retarder for slowing the movement of such a hitch toward its retracted position.
Trailer hitches for intermodal railway cars are well known in the art. They are used on "piggy back" intermodal railcars to secure over-the-road trailers on the railcar. Of late, railroads have created facilities for handling intermodal shipments. There, trailers are lifted on and off the car using either a bridge crane straddling the track, or a large side lift. In certain applications, and to give shippers greater flexibility, certain intermodal cars are capable of handling large shipping containers as well as over-the-road trailers. Since the railcar has this dual use capability, the trailer hitch must be retractable so as not to interfere with a container when the railcar is used to transport containers. These conventional hitches are manually raised either through use of a operated screw jack mechanism, or by a crane which lifts the retracted hitch.
Typically, a retractable hitch includes a first or generally vertical strut and a second or diagonal strut. The upper ends of the struts are pivotally connected to a hitch head which serves as a fifth wheel. The head supports the front end of a trailer and positively holds it on the railcar. The hitch head has releasable jaws which positively engage the king pin of the trailer. At the destination, the hitch head is operated to release the kingpin and thereby permit the trailer to be off-loaded.
Besides manually operable or crane operable retractable hitches such as described above, another commonly known hitch is a tractor operated hitch. In a well recognized alternative to employing a crane or other lifting equipment to load and off-load trailers from an intermodal railway car, a "circus" car loading/off-loading technique is used. A trailer coupled to a tractor is driven lengthwise onto the railcars, and from one car to another, until reaching a desired position. The tractor engages a retracted hitch on the car, raises it, and transfers the trailer from the tractor to the raised hitch. During off-loading, the tractor actuates a retraction mechanism for the hitch and transfers the trailer from the hitch to the tractor while the hitch moves to its retracted position. Various crane operated, and tractor operated hitches and hitch heads are shown in U.S. Pat. Nos.: 4,185,564, 4,193,350, 4,216,726, 4,221,397, 4,225,276, 4,230,430, 4,230,431, 4,239,429, 4,264,250, 4,397,594, 4,407,617, and 4,563,117.
In recent years, an intermodal railcar has been developed which is known as a "spine-type" car. This car has a center through sill beam running the length of the car. The car also has intermittent platforms at its sides for supporting the wheels of an over-the-road trailer. A hitch is provided on the spine structure for supporting the forward end of the trailer. Typically, each intermodal spine-type car carries five (5) over-the-road trailers. Because these spine-type cars are also used to carry containers, the hitch must be retractable.
Generally, since the retractable hitches used on these dual use cars are relatively heavy (e.g., 1500 pounds), these hitches tend to rapidly fall toward their retracted position. To give train personnel adequate time to move clear of the hitch, a retarder is provided to slow down the hitch. Even with these retarders, there is still a need to protect personnel from injury from the hitch as the hitch is raised and lowered. Yet, these protective measures should not interfere with the operation of the hitch.